The broad aim of this proposal is to address the functional importance of cell surface heterogeneity in cellular processes, particularly signal transduction. This research will focus on the lateral mobility of the acetylcholine receptor (AChR) in developing muscle cells, both before and after cells are induced to develop AChR clusters. Cluster formation, an early event in the developing post-synaptic junction, can be induced by applying coated latex beads to the cells. We will use single particle tracking (SPT) and laser dragging experiments to study AChR mobility. Specific aims include l) Characterization of AChR mobility using SPT to probe cell surface organization. 2) Determination of the mechanism of AChR transport to cluster sites, and whether signal transduction following bead induced clustering leads to altered mobility of the AChR. 3) Probing mechanical and structural interactions (barriers) involved in AChR cluster formation. This work should provide insight into how cell surface organization is involved in signal transduction, and the regulation of molecular interactions.